As if adolescence weren’t painful enough, legions of teenagers also suffer merciless bullying by classmates.

Nothing new there: Bullying has probably gone on in schools since the first classrooms opened.

Still, can a civilized society finally take steps to suppress abusive behavior that damages lives so young?

The documentary Bully seeks to air the issue through the stories of five bullied children in rural American towns — with two of the boys, ages 11 and 17, having already committed suicide to escape their agony.

The others include a girl who enjoyed athletic success until, after she announced she was gay, she endured ostracism by classmates and even school officials; and a girl who, having reached her limit, took a gun onto a school bus to threaten her tormentors and was detained, facing numerous felony charges.

The most prominent is Alex, a 14-year-old whose features inspire taunts about his “fish face.” As shown in footage, he is regularly punched, pummeled and stabbed with pencils while riding a school bus. His father advises him to fight the bullies, but such a reaction doesn’t suit his nature.

Worst, perhaps, is that Alex admits he barely feels emotions any longer. When his parents, having seen the bus video, take their concerns to a school administrator, they receive shrugs, platitudes and vague promises of action.

“Nothing gets done,” his mother complains.

The recurring reaction of the adults “in charge” is: “Kids will be kids,” as if that normalizes abusive behavior.

Bully packs emotional power, especially in the heart-rending testimony of the parents of the boys who killed themselves. Yet by concentrating solely on the bullied — the film might more accurately be titled Victim — director Lee Hirsch only skims the subject without exploring practical remedies.

Alex’s bullies and their parents are not confronted, and no psychologist or sociologist appears to cite findings in what must by now be a broad field of study. The viewer is left with questions: Is being predatory an instinct or a learned behavior? Are the tormentors themselves victims of bullying? Do bullies grow out of their sadistic ways?

Although Bully isn’t as thorough as it should be, it might prove effective in expanding the debate — even if one suspects that the insensitive children who most need to see it probably won’t unless they’re forced to by their schools.

The film has received welcome publicity after it was given an R rating for a half-dozen obscenities. The distributor has since decided to leave out some of those words to get a PG-13 (although the print screened this week for critics had the profanity intact). The rating change means that the kids who know the topic too well will be allowed to see it and, with hope, influence one another.